This invention relates to positively expandable and collapsible cores used in molding plastic articles having internal surfaces that include threads, grooves, recesses, perforations or other undercut shapes formed in whole or in part by a core that includes longitudinal segments arranged about a longitudinally extending core pin. Certain adjacent segments are in contact within the mold cavity and define contiguous mold surfaces for a corresponding inner wall surface of the molded part. To separate the core from the molded part those contacting segments are moved radially inwardly. One type of core wherein adjacent contacting segments are collapsed radially inwardly to permit retraction as exemplified by U.S. Pat. No. 3,660,001 to Roehr is subject to the limitation that it requires flexing of the segments. Other cores wherein adjacent segments collapse radially inwardly, as exemplified by U.S. Pat. Nos. 3,339,242 or 3,482,815 or 3,584,111 or 4,130,264 are subject to limitations both as to costs and operation because they require complex sliding structures for guiding and/or effecting the radial inward movement of the contiguous core segments.
It is an object of this invention to provide a radially inwardly collapsible core wherein contiguous segments are pivoted for rocking movement without the imposed condition of flexing with its inherent limitations, and wherein the mounting and the actuation of the segments is effected in a simple, economical, and reliable manner.
It is further object of this invention to provide an inwardly collapsible core wherein adjacent segments are mounted for rocking movement between their alternate positions by a movable actuator-pin (or pins) wherein the actuator pin holds the segments in their molding positions and, preparatory to the movement of the adjacent segments to their alternate positions it first frees that hold and then initiates the rocking movement to the alternate position.
It is a still further object of this invention to provide an inwardly collapsible core of the above mentioned type wherein the actuating pin has separate camming surfaces for causing each of the segments to rock in its two respective directions, and those surfaces are spaced apart so that upon movement of the actuator in a direction reverse from its previous movement there is a delay in causing a reverse rocking of the molding segments. This assures clearance for the movement of the segments and the actuating pin.